Portable electronic devices, or simply portable devices, are battery powered. Many such devices are powered by rechargeable batteries or battery packs because the device uses so much energy that it would be cost prohibitive to constantly replace spent non-rechargeable battery cells. For example, cellular telephones and portable two-way radio devices typically use rechargeable battery packs because of how much energy they use. There are a variety of rechargeable battery technologies that are popular and presently in use. Generally, it is desirable to have the highest energy storage density, referred to as charge capacity, because it allows for the smallest battery for a given expected usage time.
Among the well-known battery technologies presently in popular usage, lithium ion (Li-ion) batteries are one of the more popular technologies because of their high energy storage density, making them especially popular for portable devices that are routinely carried, such as communication devices. However, Li-ion batteries are subject to certain operating limitations which, if exceeded, can greatly shorten the life of the battery, referring to the number of charge/discharge cycles. One parameter that is of particular concern is the undervoltage limit. The undervoltage limit is the lowest voltage that the battery should be allowed to drop to during discharge. Allowing the voltage to drop lower than the undervoltage limit can reduce the battery life. To prevent an undervoltage condition, some portable devices sense the battery voltage, and when the battery voltage drops to the undervoltage limit, shut themselves off, or shut off most of the device so as not to continue to discharge the battery below the undervoltage limit, even though the electronics can continue to operate at voltage levels below the undervoltage limit. The portable device maintains itself off, ignoring attempts by the user to turn the portable device back to an operating state, until the battery is recharged or removed and replaced.
Another issue that affect portable devices is intermittent battery contact. Typically a battery is attached to a portable device using a plurality of contacts. A contact is an electrically conductive element that presents a surface that mates with a corresponding contact, and the two contacts are generally urged or held against each other by, for example, a spring means. As a result, when the portable device (with the battery attached) experiences a momentary mechanical shock, such as upon being dropped, the contacts that are normally touching to provide an electrical connection can momentarily lose contact. When that happens, a portable device designed to shut itself off upon an undervoltage condition could shut itself off, mistaking the momentary loss of battery contact for an undervoltage condition. Given the critical need for continuous operation of some portable devices, such as two-way radio devices used by law enforcement, public safety, rescue, and military personnel, having a device shut itself off upon experiencing a momentary shock could be detrimental.
Accordingly, there is a need for a method and apparatus for distinguishing momentary loss of battery contact from an undervoltage condition in a portable device.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.